The British government will lose its leadership position on climate change and risk scuppering a global deal to cut emissions if it presses ahead with a new generation of dirty coal power, say leading US scientists and environmental leaders.

The heads of three influential groups, representing more than 2 million members, have written to the foreign secretary, David Miliband, warning that the UK proposals for up to eight coal plants threaten the chance of the US joining a post-Kyoto international agreement, due in 2009.

It is the first public sign of growing international anger over the plans and will add to pressure on Miliband and environment secretary Hilary Benn to oppose the government's new coal policy in cabinet. Most immediate is the decision on a new coal plant at Kingsnorth in Kent, the site of this month's Climate Camp protest.

There has been heavy criticism of the plans to build coal plants without technology to capture and bury their large volumes of carbon dioxide. The letter, revealed to the Guardian, is signed by the heads of the Sierra Club, the Union of Concerned Scientists and the Natural Resources Defence Council. It argues Britain is in a particularly important position because of "your government's historic commitment to lead on global warming in Europe and around the world".

Energy minister Malcolm Wicks said: "As a 'live' planning case I cannot comment on the merits or otherwise ... or on the timing of any decision." In a Guardian interview this month, he said new coal power stations were essential for energy security and to allow development of carbon capture technology. Without that technology, "all is lost on global warming", he said, because of China's reliance on coal.